INFLUENCE OF BENTHIC BOUNDARY-LAYER FLOW ON FEEDING RATES OF CILIATES AND FLAGELLATES AT THE SEDIMENT-WATER INTERFACE

Heterotrophic protists are integral to microbial food webs, yet factors determining their activities at the sediment-water interface (SWI) are poorly understood. We measured effects of bed shear stress on uptake of suspended bacteria by cultured ciliates and natural communities of protists at the SWI in a flume. Clearance rate of a euplotid ciliate was directly related to friction velocity (u*) up to 1.0 cm/s, followed by a reduction at u* of 1.5. Clearance rate of a scuticociliate was unrelated to u*. Data from additional species will be presented. Species differences may be due to interaction of flow with feeding mechanisms or to behavior. Experiments with field sediment cores revealed a community-level response to flow. From u* of 0 to 0.9 cm/s, the clearance rate of flagellates increased slightly and that of ciliates increased several fold. Boundary-layer flow creates a dynamic link between microbial food webs of the plankton and benthos by controlling suspension-feeding rates at the SWI. Feeding may have tidal periodicity, and protistan productivity may differ among sites according to flow regime.